This invention relates to a housing for a video, audio or other tape cassette which includes a lid protecting the run of the tape extended at the front of the housing and a lid locking member for controlling the lid motion. More particularly, it concerns a construction capable of preventing excessive turning of the lid locking member at the time the lid is turned open.
Cassettes holding a video tape or the like are provided with a front cover, known as lid, over the front opening of the housing. When the cassette is not in use, the lid keeps the front opening closed under the urging of a spring so as to cover and protect the otherwise exposed run of the tape. This prevents intrusion of dust from the front into the cassette and precludes the possibility of damaging or staining the tape with fingerprints, grease or the like at the time of cassette handling. Should such damaging or staining occur, signal occurs would result, leading to distorted images in the case of a video tape or sound skipping in an audio tape. Nevertheless, the tape cassette with the construction described is still partly open, at the front of the bottom of the casing, in order to be ready for cassette loading into the recorder. The front bottom corner remains open even when the cassette is unused, thus allowing dust intrusion through that opening. If the construction is used in a video tape cassette without modification, significant errors could result in the course of recording or playback because the video signals are highly susceptible to the influence of dust and other foreign matter. In view of this, the prevention of dust intrusion through the front bottom opening has been a problem of urgent importance. As an attempt to solve it, an improved construction, shown as exploded in FIG. 2, has already been developed. In the figure, the number 10 indicates an upper half housing section, 12 a lower half housing section, and 14 a front lid. Inside the space defined by these housing parts are accommodated other components such as a supply reel 16 and a take-up reel 18. A length of magnetic tape 20, contained on the supply reel 16, is adapted to be gradually moved to and accumulated on the take-up reel 18. The path of the magnetic tape extends from an opening formed near the right side walls of the upper and lower half housing sections 10, 12 to an opening formed near the left side walls, through a route in front of the front opening of the housing combinedly formed of those housing halves. The conventionally employed front lid 14 covers the exposed run of the magnetic tape 20 at the front side. Behind this front lid 14 is located a newly added inner lid 22, which covers the rear side of the tape to avoid intrusion of dust from below the front bottom corner of the housing. A lid locking member 24 is mounted, together with a lock spring 26, in the vicinity of the mating portions of the right side walls of the upper and lower half housing sections 10, 12. The lid locking member 24 functions to lock the front lid 14 and the inner lid 22 when the two lids close the front opening of the housing and release the lids when they are turned to open the housing. The lock spring 26 normally biases the lid locking member 24 to lock the lid 14, while forcing the member to turn about its axis.
FIG. 3 shows the lid locking member and its lock spring of FIG. 2 on an enlarged scale. The lid locking member, formed of a piece of plate, has a locking leg lever 28 and a releasing leg lever 30. The locking leg lever 28 projects perpendicularly frontward from the edge of the lid locking member 24 and then turns upward like a hook. The releasing leg lever 30 slightly projects perpendicularly frontward and then shifts sidewise, this time projecting perpendicularly outward from the planar wall portion. The lid locking member 24 further comprises a head 32 and a pivot 34 formed at a central point near the head 32. The pivot 34 is columnar-shaped and projects perpendicularly from the planar wall of the member 24. It is surrounded down to its root by a recess 36 for accommodating the lock spring 26. The axis 38, passing through the center of the pivot 34, is spaced a distance A from a parallel line extended from the crown of the head 32. The numberal 40 indicates a provisional stopper slightly projecting sideways from the planar wall of the lid locking member 24 for temporarily keeping the member from turning to excess.
FIG. 4 is an inside view of a fragment of the upper half housing section constituting the region for accommodating the lid locking member shown in FIG. 2. The numeral 42 designates the region where the lid locking member 24 is to be mounted. The region 42 has an inner wall 44, outer wall 46, and a rear wall 48, forming a slot 50, in which the lid locking member 24 is fitted and set in position. Bearing recesses 52 (52a, 52b) are formed in the inner and outer walls 44, 46 to support the pivot 34 of the lid locking member. Mirror image bearing recesses are formed in the lower half housing section 12 to mate the above recesses when the housing is assembled. The common centerline 54 of the bearings and the rear wall 48 are spaced apart a distance B. When this distance B is compared with the distance A between the center of rotation of the pivot 34 of the lid locking member 24 and the crown of the head 32, the relation B&gt;A holds.
The act of setting such a video tape cassette in a recorder first forces the releasing leg lever 30 back to unlock the lid 14 that closes the front opening of the cassette. Then, with the turning of the lid locking member 24, the locking leg lever 28 keeping the lid 14 locked under the urging of the lock spring 26, with its hook end in engagement with a projection on a side wall of the lid 14, is disengaged. At the same time, the lid 14 turns fully to uncover the front opening of the housing. The housing having been opened, the releasing leg lever 30 is set free, and the lid locking member 24 is reset by dint of the lock spring 26 to the locking position. There is no possibility of its hook end engaging the projection on the side wall of the lid 14 since the lid has already concluded its turning motion. However, if the cassette is accidentally subjected to any excessive vibration of impact during the turn of the lid 14, the lid locking member 24 might turn too far in the locking direction, causing the releasing leg lever 30 to find its way wrongly into a gap formed between the side wall edge and the outer wall surface of the lower half housing section 12. Should this happen, the lid 14 would fail to return to the initial position and close the housing after the use of the cassette, because the lid turning in the locking direction would hit against the releasing leg lever 30 and be kept from further turning. In ordinary service conditions, of course, the provisional stopper 40 on the plate surface of the lid locking member comes in contact with the projection 41 formed on the inside of the outer side wall of the lower half housing section 12, as seen in FIG. 5, so as to keep the member from turning too far, beyond a given point, in the locking direction. However, the stopper 40 has a limitation in structure because of the necessity of inserting the lid locking member into the slot 50 for assembling. The stopper being simply designed as a provisional stop, excessive turning of the member can widen the gap between the inner and outer side walls until the member is disengaged from the projection of the outer wall. Thus, if the lid 14 fails to return to the original position, it would become difficult to take out the cassette from the recorder. A forcible attempt to take it out could fatally damage the tape, cassette, and even the recorder. Such excessive turning of the lid locking member 24 can also be caused by manual handling of the cassette.